Effects of Non-Conventional Sterilisation Methods on PBO-Reinforced PVA Hydrogels for Cartilage Replacement.

Articular cartilage (AC) degradation is a recurrent pathology that affects millions of people worldwide. Polyvinyl alcohol (PVA) hydrogels have been widely explored for AC replacement. However, their mechanical performance is generally inadequate, and these materials need to be reinforced. Moreover, to be used in a clinical setting, such materials must undergo effective sterilisation. In this work, a PVA hydrogel reinforced with poly(p-phenylene-2,6-benzobisoxazole) (PBO) nanofibres was submitted to three non-conventional sterilisation methods: microwave (MW), high hydrostatic pressure (HHP), and plasma (PM), in order to evaluate their impact on the properties of the material. Sterilisation was achieved in all cases. Properties such as water content and hydrophilicity were not affected. FTIR analysis indicated some changes in crystallinity and/or crosslinking in all cases. MW was revealed to be the most suitable method, since, unlike to PM and HHP, it led to a general improvement of the materials' properties: increasing the hardness, stiffness (both in tensile and compression), and shear modulus, and also leading to a decrease in the coefficient of friction against porcine cartilage. Furthermore, the samples remained non-irritant and non-cytotoxic. Moreover, this method allows terminal sterilisation in a short time (3 min) and using accessible equipment.

PVA-Based Hydrogels Loaded with Diclofenac for Cartilage Replacement.

Polyvinyl alcohol (PVA) hydrogels have been widely studied for cartilage replacement due to their biocompatibility, chemical stability, and ability to be modified such that they approximate natural tissue behavior. Additionally, they may also be used with advantages as local drug delivery systems. However, their properties are not yet the most adequate for such applications. This work aimed to develop new PVA-based hydrogels for this purpose, displaying improved tribomechanical properties with the ability to control the release of diclofenac (DFN). Four types of PVA-based hydrogels were prepared via freeze-thawing: PVA, PVA/PAA (by polyacrylic acid (PAA) addition), PVA/PAA+PEG (by polyethylene glycol (PEG) immersion), and PVA/PAA+PEG+A (by annealing). Their morphology, water uptake, mechanical and rheological properties, wettability, friction coefficient, and drug release behavior were accessed. The irritability of the best-performing material was investigated. The results showed that the PAA addition increased the swelling and drug release amount. PEG immersion led to a more compact structure and significantly improved the material's tribomechanical performance. The annealing treatment led to the material with the most suitable properties: besides presenting a low friction coefficient, it further enhanced the mechanical properties and ensured a controlled DFN release for at least 3 days. Moreover, it did not reveal irritability potential for biological tissues.

Development of polycarbonate urethane-based materials with controlled diclofenac release for cartilage replacement.

Hydrogels are very promising human cartilage replacement materials since they are able to mimic its structure and properties. Besides, they can be used as platforms for drug delivery to reduce inflammatory postsurgical reactions. Polycarbonate urethane (PCU) has been used in orthopedic applications due to its long-term biocompatibility and bio-durability. In this work, PCU-based hydrogels with the ability to release an anti-inflammatory (diclofenac) were developed, for the first time, for such purpose. The materials were reinforced with different amounts of cellulose acetate (CA, 10%, 15%, and 25% w/w) or carbon nanotubes (CNT, 1% and 2% w/w) in order to improve their mechanical properties. Samples were characterized in terms of compressive and tensile mechanical behavior. It was found that 15% CA and 2% CNT reinforcement led to the best mechanical properties. Thus, these materials were further characterized in terms of morphology, wettability, and friction coefficient (CoF). Contrarily to CNTs, the addition of CA significantly increased the material's porosity. Both materials became more hydrophilic, and the CoF slightly increased for PCU + 15%CA. The materials were loaded by soaking with diclofenac, and drug release experiments were conducted. PCU, PCU + 15%CA and PCU + 2%CNT presented similar release profiles, being able to ensure a controlled release of DFN for at least 4 days. Finally, in vitro cytotoxicity tests using human chondrocytes were also performed and confirmed a high biocompatibility for the three studied materials.

Additive manufacturing of ceramics for dental applications: A review.

OBJECTIVE: The main goal of this review is to provide a detailed and comprehensive description of the published work from the past decade regarding AM of ceramic materials with possible applications in dentistry. The main printable materials and most common technologies are also addressed, underlining their advantages and main drawbacks. METHODS: Online databases (Web of knowledge, Science Direct, PubMed) were consulted on this topic. Published work from 2008 to 2018 was collected, analyzed and the relevant papers were selected for inclusion on this review. RESULTS: Ceramic materials are broadly used in dentistry to restore/replace damaged or missing teeth, due to their biocompatibility, chemical stability and mechanical and aesthetic properties. However, there are several unmet challenges regarding their processing and performance. Due to their brittleness nature, a very tight control of the manufacturing process is needed to obtain dental pieces with adequate mechanical properties. Additive manufacturing (AM) is an emerging technology that constitutes an interesting and viable manufacturing alternative to the conventional subtractive methods. AM enables the production of customized complex 3D parts in a more sustainable and less expensive way. AM of ceramics can be achieved with an extensive variety of methods. SIGNIFICANCE: There is no perfect technology for all materials/applications, capable alone of fulfilling all the specificities and necessities of every patient. Although very promising, AM of ceramic dental materials remains understudied and further work is required to make it a widespread technology in dentistry.

On the influence of Streptococcus salivarius on the wear response of dental implants: An in vitro study.

This study aims to understand microorganisms' effect and relevance of aseptic conditions on wear performance of dental materials. Tribocouple zirconia/titanium was submitted to tribological tests in the presence of Streptococcus salivarius biofilm, the most abundant bacteria in the oral cavity. Reciprocating ball-on-plate tests were carried out at 37°C, pH 7, 2 N, and 1 Hz, during 2 h, using Ti6Al4V balls as pins and Y-TZP plates. Simultaneous OCP readings assessed corrosion tendency. Tested lubricants were artificial saliva, artificial saliva plus glucose, and artificial saliva plus glucose and S. salivarius. Wear volume and worn surfaces were analyzed after test. S. salivarius proliferation was enhanced in artificial saliva plus glucose. When a highly populated biofilm was present at the zirconia/titanium interface, titanium wear decreased by ~60% compared to artificial saliva and artificial saliva plus with glucose, respectively, with 0.0060 and 0.0053 mm3 loss. Wear was not observed in zirconia under any tested condition. Presence of S. salivarius also decreased corrosion activity during wear. Lowest free OCP value reached during sliding was -260 mV in artificial saliva, -246 mV in artificial saliva plus glucose, and -196 mV in artificial saliva plus glucose and bacteria. This decreased to -147 mV when a highly-populated S. salivarius biofilm was present at the interface. Overall, obtained results show that the presence of S. salivarius clearly changes the corrosion-wear performance of the tested dental materials, confirming that it must be recognized, and that asepsis level and conditions during wear test of dental materials must be clearly established and controlled to ensure reproducible results and supported conclusions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1393-1399, 2019.